Here my 2 cents after a lot of hosting games in québec.
I put the tentative for now in the roster and player have to confirm 2 week prior to the events, if not confirmed i remove them from the roster. I do that only for player i know that are actually be there, other won't even be asked to play.
In the after action reports i put the last signup roster : and i put comments and color to it. So everybody know what you did ( Being late, leaving early, not showing up or given weird reason. ).
If everybody see it, it give a lot more punch than only host in a private forum, trust me. the team will be pointed out, the friend gonna be reminded that his firend is not thrustworthy and so on. The pressure will come to this player from everywhere and this is working.
this year i have over 95% of attentance.. With 1 game of 89 players out of 90 who were signup.
We also screen player, we choose who can come, and if you have been seen to flaked out, guess what.
I also tried pre-payment in the past, the result was better, but nevertheless i still have gotten 10-12 players who did flaked out.
There is a game organizer here in quebec for host. The programmer will add the flaker rating to it on the next version.. the tool already exist in french. it could be translated i guess.
I will begin to use it for all game next year.